Is it Open Mike or Open Mic?
Answer: The correct spelling is "Open Mic"
"Mic" is the shortened form of the word "Microphone", the primary tool of a stage. It amplifies the voice and represents power, so it is often fiercely guarded. However, an open mic is very special, it is an open opportunity to take that stage and hold the power for just a moment.
"Mike" — on the other hand — is the informal short form of the male name "Michael". If the phrase were spelt "Open Mike" it would imply a person named Micheal who is open, perhaps to trying new things. Why would you need to find an Open Mike? Perhaps you are curious to try BASE jumping, take part in a bufo ceremony or attend a tantric sex workshop, but due to a deep-seated superstition, you would only be comfortable doing this when accompanied by someone named Michael.
To clarify, this website does not publish the geographic location and availability dates of curious men named Michael. So the spelling is Open Mic.